This application claims the benefit of Japanese Applications 2001-080635, filed Mar. 21, 2001, and 2002-061485, filed Mar. 7, 2002, the entireties of which are incorporated herein by reference.
The present invention relates to a lithium secondary cell (hereinafter simply referred to as xe2x80x9ccellxe2x80x9d) and a lithium secondary cell connecting structure (hereinafter simply referred to as xe2x80x9cconnecting structurexe2x80x9d), and more particularly, to a lithium secondary cell and a lithium secondary cell connecting structure capable of preventing a lowering of performance due to the use and extending its service life.
Lithium secondary cells are widely used as power supplies for portable communication apparatuses and electronic devices such as notebook personal computers in recent years. Furthermore, the development of lithium secondary cells is underway as motor drive batteries for electric vehicles and hybrid electric vehicles (hereinafter simply referred to as xe2x80x9celectric vehicle, etc.xe2x80x9d) in response to a growing international demand for resource saving and energy saving to protect the global environment. This lithium secondary cell is used for a connecting structure made up of a plurality of cells connected in series to secure a voltage necessary to drive the motor. Since the service life of an electric vehicle, etc. is estimated to be about 5 to 10 years, this lithium secondary cell and the lithium secondary cell connecting structure are expected to have their service life equivalent to that of the electric vehicle, etc.
This lithium secondary cell has a high operating voltage and high energy density, having an advantage of being able to discharge a high current, while it has a disadvantage of generating great heat, liable to cause a temperature rise of the battery. This temperature rise due to heating is attributable to inner resistance of the inner electrode body generated when a current flows. When the inner electrode body is continuously exposed to a high temperature state caused by the temperature rise, its internal resistance further increases, which causes the inconvenience of eventually reducing the battery capacity and drastically reducing performance.
However, despite such inconvenience of the lithium secondary cell, it is the current situation that heating prevention measures are not taken sufficiently accompanied by problems of an inevitable lowering of performance due to the use and short service life. Furthermore, the lithium secondary cell connecting structure needs to provide space between cells to facilitate the heat dissipation of each lithium secondary cell, which causes a problem of poor volumetric efficiency of the connecting structure.
The present invention has been implemented in view of the above-described conventional problems and it is an object of the present invention to provide a lithium secondary cell and a lithium secondary cell connecting structure intended to prevent heating of the lithium secondary cell and the lithium secondary cell connecting structure to maintain their temperature within an appropriate range so as to prevent a lowering of the performance due to the use and extend their service life.
That is, the present invention provides a lithium secondary cell comprising: an inner electrode body impregnated with a non-aqueous electrolyte, made up of a positive electrode and a negative electrode wound or laminated together with a separator inserted in between, a cell case that contains the inner electrode body and an electrode cover that seals the inner electrode body provided with a cell cover, external terminals and internal terminals characterized by including a means for cooling the electric current path. In the present invention, it is preferable that the electric current path includes the external terminals.
According to the present invention, there is further provided a lithium secondary cell comprising: an inner electrode body impregnated with a non-aqueous electrolyte, made up of a positive electrode and a negative electrode wound so as to surround an outer wall of a core with a separator inserted in between, and a cylindrical cell case that coaxially contains the inner electrode body; wherein a heat conductivity ratio (X/Y) of a heat conductivity (X) in a direction of the center axis to a heat conductivity (Y) in a direction of a diameter of the lithium secondary cell is 50 or more. In the present invention, it is preferable that the heat conductivity ratio (X/Y) is 100 or more.
This configuration condition is ideally applicable to a lithium secondary cell having a capacity of 2 Ah or more and ideally mounted on a vehicle to start an engine and ideally used for an electric vehicle or hybrid electric vehicle.
Furthermore, the present invention provides a lithium secondary cell connecting structure constructed of a plurality of lithium secondary cells connected in series and/or in parallel by means of a bus bar, with the lithium secondary cell comprising an inner electrode body impregnated with a non-aqueous electrolyte, made up of a positive electrode and a negative electrode wound or laminated together with a separator inserted in between, a cell case that contains the inner electrode body and an electrode cover that seals the inner electrode body provided with a cell cover, external terminals and internal terminals, characterized by including a means for cooling the electric current path. In the present invention, it is preferable that the electric current path includes the bus bar.
This configuration condition is ideally applicable to a lithium secondary cell having a capacity of 2 Ah or more and ideally mounted on a vehicle to start an engine and ideally used for an electric vehicle or hybrid electric vehicle.